s3-object-response

This middleware is a Proof of Concept and requires real world testing before use, not recommended for production

Fetches S3 object as a stream and writes back to s3 object response.

Install

To install this middleware you can use NPM:

npm install --save @middy/s3-object-response
npm install --save-dev @aws-sdk/client-s3

Options

• AwsClient (object) (default S3Client): S3Client class constructor (i.e. that has been instrumented with AWS XRay). Must be from @aws-sdk/client-s3.
• awsClientOptions (object) (optional): Options to pass to S3Client class constructor.
• awsClientCapture (function) (optional): Enable XRay by passing captureAWSv3Client from aws-xray-sdk in.
• disablePrefetch (boolean) (default false): On cold start requests will trigger early if they can. Setting awsClientAssumeRole disables prefetch.

NOTES:

• The response from the handler must match the allowed parameters for S3.writeGetObjectResponse, excluding RequestRoute and RequestToken.
• XRay doesn’t support tracing of fetch, you will need a workaround, see https://github.com/aws/aws-xray-sdk-node/issues/531#issuecomment-1378562164
• Lambda is required to have IAM permission for s3-object-lambda:WriteGetObjectResponse
• context.s3ObjectFetch is a pending fetch Promise kicked off in the before hook. Your handler must await it — otherwise a network/404/auth failure surfaces as an unhandled promise rejection rather than as a caught error in your handler. The samples below show the correct pattern.

Sample usage

Stream

import zlib from 'zlib'
import middy from '@middy/core'
import s3ObjectResponse from '@middy/s3-object-response'
import {captureFetchGlobal} from 'aws-xray-sdk-fetch'

captureFetchGlobal(true) // Enable XRay

const lambdaHandler = (event, context) => {
  const readStream = await context.s3ObjectFetch.then(res => res.body)
  const transformStream = zlib.createBrotliCompress()
  return {
    Body: readStream.pipe(transformStream)
  }
}

export const handler = middy().use(s3ObjectResponse()).handler(lambdaHandler)

JSON

import zlib from 'zlib'
import middy from '@middy/core'
import s3ObjectResponse from '@middy/s3-object-response'

const lambdaHandler = async (event, context) => {
  let body = await context.s3ObjectFetch.then((res) => res.json())
  // change body
  return {
    Body: JSON.stringify(body)
  }
}

export const handler = middy().use(s3ObjectResponse()).handler(lambdaHandler)

Bundling

To exclude @aws-sdk add @aws-sdk/client-s3 to the exclude list.